Neural circuitry underlies human behavior in all of its forms. Aberrant states in the nervous system, both acute and chronic are the cause of mental health diseases that affect more than a quarter of Americans over the age of 18. 'Executive' regions such as the dorsolateral prefrontal cortex (dlPFC) in humans (approximately equivalent to the medial prefrontal cortex (mPFC) in rodents) are the subject of particular interest as functional imaging, electrophysiological, and post-mortem studies of humans have shown cellular and neurophysiological abnormalities in those regions are associated with psychiatric disorders (e.g. schizophrenia, mood disorders, and addiction). The great complexity of the dlPFC in addition to its interplay with many different brain regions has made distinguishing particular pathological neural circuitry to these diseases extremely difficult. How can we probe the nervous system to understand how activity patterns in neural circuits lead to behavior? Can we then better understand pathological states? In order to tackle such problems, our laboratory has devised ways of optically activating and silencing neurons in specific neuronal subtypes based on their genetic signatures, (e.g. CaMKII-alpha as a marker for excitatory pyramidal neurons or parvalbumin in a subset of inhibitory neurons), using light gated ion channels and pumps, a method termed 'Optogenetics'. In the first part of this proposal, we aim to expand on these technologies by utilizing the unique features of light activation of such proteins by using two-photon (2P) microscopy in order to attain specificity beyond genetic signatures; more specifically, this project will achieve spatially restricted activation and silencing of the nervous system at the resolution of a single cell (2P optogenetics). Further, we will use 2P activation of individual neurons for high-throughput mapping of functional neuronal connectivity in layer V of mPFC of different neuronal subtypes in order to better understand how they function as a unit. This part of the proposal will also show this tool's generalizability to all areas of the brain using ex vivo preparations, which will provide a wealth of information for researchers investigating both normal and pathological nervous system states. In the second part of this project, we will use 2P optogenetics to understand dynamic cortical function in the mPFC. Local cortical processes such as synchrony whose dysfunction has been implicated in psychiatric disorders (e.g. schizophrenia) will be investigated to understand the underlying cellular and network mechanisms that lead to these phenomena. Taken together, these tools will hopefully lend insight into the functional connectivity matrix between different neurons in the mPFC and how they work together to provide efficient processing of information that gives rise to behavior.